Crack , crack not ?

[Alfapillar]

hi guys,

i've found this on a repainted machine, is it a paint crack or the boom is definetly cracked ? :beatsme the " crack " is not deep, i've got different point of view, some told me it's not a crack and other it's a crack ointhead
if anyone can help on this !!! if need more photos no problem :drinkup

 

[MKTEF]

Only way to be shure about your question is to get a quality controller to bring his weld controlling equipment and check.
Ultrasound equipment will get U the answer imediately.

But it looks like the area has been welded/worked on under the paint.
That stripe might be a smal crack just in the surface of the weld.
If so, it shurely is not a quality weld made there...
I would quess lack of preheating or to quick cooling, so the tension/stress in the weld was so high it cracked after som use.

In your 1.pic it looks to be a area where the thicknes of the plate is increased/decreased towards the big weld. Then it can shurely be a area where a crack would appear.

I don't think u got so much movement in that area to get a paint crack there.
But if the paint is real thick in that area, it can be a crack in the paint.
We are then talking about several millimeters thick paint

Next question is if it matters?
I would say yes, only a smal crack may be the startingplace for a big problem later.
Sourface should bee smooth to avoid the stress beeing buildt up under/in the crack.
How long it takes before it gets real bad is impossible to say.
Carefull use and it might last long, heavy use and it can break real quick.

If u tell us which machine and age, i bet somebody here can give us some experience in that area.
Looks to be in right by the main bolt for the boom.
There is some pics in the thread "Norway pics" from a komatsu PC750 with a broken boom in that area.

 

[OneWelder]

Boom /stick cracks tend to grow a lot better than my garden did this summer!
Can not be sure from that picture.
You may have some Bondo ,Trying to cover up an unsuccessful repair - not all that uncommon with stuff run through an auction
A grinder would answer all

 

[385c JR]

Hello Alfapillar.
It looks like a cat machine. Am I right?
In that case, I would be a litle sceptical.
I'll showe you som pics of our cat 345c
Dont know if you get some answer of this, but it's my experience that if you see somthing looks like a crack in the boom off a cat, you should replace it asap... :usa

 

[brian falcone]

crack

on a few 320 and 315 machines ive seen they tend to crack behind the boom piston mounts. ive seen sticks crack just below the pin that hold them to the boom. our 320l has a paint crack at the end of the boom that i marked with a marker when we bought it...its been 4 years and a lot of hours later and it hasnt spread. the line in the pic is allmost the entire thickness of the boom. id have it looked at before id buy it.

 

[ncbschzzt]

Take a small grinder and clean away some of the paint. You will clearly see a crack if it is there. No reason to bring out ultrasound equipment, this should be very easy to diagnose. Now the repair on the other hand well that will be a little tougher.

 

[John C.]

It's too straight to be just a crack in the boom. Also being that wide it would have run into the top plate. I'm thinking it's Bondo.

Grind it out a little to be sure. I'll bet its power and not sparks that will fly of the wheel.

Good Luck!

 

[cat 385]

Hello Alfapillar.
It looks like a cat machine. Am I right?
In that case, I would be a litle sceptical.
I'll showe you som pics of our cat 345c
Dont know if you get some answer of this, but it's my experience that if you see somthing looks like a crack in the boom off a cat, you should replace it asap... :usa

seems like i've heard this before.

 

[stock]

Get some iron filings from a workshop with a magnet make tem all stickey apply them to the boom and watch ,if there is a crack when you stick the magnet on to the jib close to the crack the filings will allign themselves to a crack radiating from one end to the other on both sides ie like pencil arc shaped lines

 

[Alfapillar]

Thanks guy's for replying :drinkup
It's a 2000 Cat 330BL, with around 10000 Hours, the machine was parked in a sea port for more than 5 months, could it be a result of this long time parking ? :beatsme
When we buy this unit, the " crack " wasn't there, and the machine didn't work since we got it, habitually we go away from repainted unit, but on this one, the seller state that the machine don't have any crack :Banghead

maybe a stupid question what's a Bondo ?

 

[mouse]

bondo is presumably some sort of filler.

paint doesn't just crack in my experience, fillers can and do crack but not usually in such a straight line or over such a distance unless there is an underlying problem. what is very clear is it is a crack over either a repair or a weld and therefore should be investigated.

i'd hit it with an angle grinder tho the iron filings trick might be worth trying (its a new one on me)

my guess is they've done a bodgy repair on it and thrown some filler over a crack without bothering to weld it, painted the thing then offloaded it to some poor sucker (you in this case....)

good luck!

 

[OneWelder]

Bondo is autobody filler

 

[swampdog]

What seems odd is that the "crack" seems perfectly straight. Metal does not break that neatly. Either grind or scrape the paint off and you will soon find out what lies underneath. Let us know what you find.

 

[surfer-joe]

If it look like a "quack," and "quacks" like a duck, then it's a crack. I've seen many of these on Cat excavators and I'd bet the farm that you have more serious cracks in that boom. Biggest problem is that cracks of this nature can not be repaired from the outside. The real problem is inside and for that you have to remove a big enough piece of the boom side to actually be able to get inside the boom to repair the metal there that is damaged. Some folks would just repair the crack on the outside as looks like what was previously done in your picture. Others than might weld a fishplate over that in an ill-fated attempt to strengthen the boom. That doesn't work long term either.

I believe your boom has been seriously damaged and that whomever had it previously just welded up the outside and tried to make it look as though nothing ever happened. The marks under the paint point that out. Good pics by the way.

Check with your local Cat house and ask for an engineering drawing of that boom section. Those folks can also point out to you how to properly repair that section.

Good Luck!

 

[gmads01]

Just last month had the boom on our Cat 308C fall off - cracked completely thru at pin-boss. Will post pics when I'm allowed.

 

[ncbschzzt]

It's too straight to be just a crack in the boom. Also being that wide it would have run into the top plate. I'm thinking it's Bondo.

Grind it out a little to be sure. I'll bet its power and not sparks that will fly of the wheel.

Good Luck!

Its not to straight to be a crack, if there is a baffle there then a crack can be almost perfect. Seen it before, just not sure if there is a baffle there on a Cat.

 

[LowBoy]

I agree with surfer-joe on this one also. Inside the boom is another whole structural set of gussets, and there's more than likely another set of problems that lie beneath the surface.

Definitely put a grinder to it and investigate before it get's worse. Nothing uglier than a boom hanging limp off to the side...been there, done that, got that tee shirt with the hood. Had a 245 boom break off in -20 degree weather once, that was a son of a bee to get straightened out. That's where I got my education on the interior gusset system though.

 

[Turbo21835]

One company I worked at had a 320cl break a boom. Looks a lot like it was in the same general area as your picture. As surfer joe stated, it was a repair that was very involved. It required cutting out a 3 foot long section of the boom on the battery box side. Every weld inside on the other corners was redone. There was extra plate added inside. Then the outside was fitted with a new plate and welded into place. It took 1 welder about 40 hours of work.

 

[dayexco]

Definitely put a grinder to it and investigate before it get's worse..

or it breaks off and kills somebody

 

[JDOFMEMI]

You have lots of good advice already.

Do Not Operate This Machine!

It is DEFINATLEY a crack, and a bad one at that. I believe it is right where the interior gusset that spans the factory weld joint ends.
As stated, the repair will be extensive, and I would get a copy of the Cat welding proceedures and make sure they are followed.
There are probabley other hidden cracks, as I do not think the side plate can move that far without the top flange moving somewhere.